Characterization of Three Genotypes of Sweet Potato and their Suitability for Jam Making
For a thousand years ago, man by trial and error screened some materials for catering his needs. Now in the era of science and technology the scientist discovered many nutritive crops. A high beta-carotene genotypes of sweet potatoes; TDINUNG NO.64 (dark-orange flesh), CEMSA 74-228 (dark-cream flesh) and ZAPALO (pale-orange flesh) were characterized and processed to jam. Moisture, crude protein, crude fibre, ash, fats, carbohydrates and vitamin A, as well as ascorbic acid, minerals, B group and energy value of genotypes were determined. TDINUNG NO.64 increased in fiber, fats and vitamin C. CEMSA 74-228 contain highest protein, carbohydrates and energy while ZAPALO have higher ash. Moreover, sweet potatoes under study are very rich in vitamin A and containing B-complex greater than many common fruits. The effects of storage at ambient temperature, on microbial growth, TSS, pH, total acidity and total sugars were found to be significant at p≤0.05 level. As well as, the sweet potato jams had higher acceptability than the market jam especially in term of its color, taste, consistency and overall quality.
Received: February 22, 2011;
Accepted: July 25, 2011;
Published: February 27, 2012
The sweet potato (Ipomoea batatas) is starchy tuberous root is the major
economic plant of the crop (Antia et al., 2006),
sweet tasting and applications depend on its starch content (Bovell-Benjami,
2007). It probably originated in Mexico and Central America but is now grown
widely in Mediterranean-type, subtropical and tropical climatic regions of the
world (Zhang et al., 2004).
The Sudanese name for sweet potato is Bambie. The sweet potato is a
herbaceous perennial vine with alternate heart-shaped. It is white, yellow,
orange or purple flesh and its skin may be red, purple or brown and white in
color (Zhao et al., 2005). The food ranking system
also showed sweet potato to be a strong performer in terms of traditional nutrients.
This root vegetable has been used in the traditional system of medicine for
Alzheimer's disease because which is rich in beta-carotene (Roy
et al., 2008). A very good source of Vitamin C and manganese, as
well as a good source of copper, dietary fiber, vitamin B6, potassium and iron.
Moreover, poor in content of protein but which is present contains several of
essential amino acids like leucine, lysine, phenylalanine, valine, tryptophan
and threonine (Hussain et al., 2008). Sweet potatoes
and its leaves contain antioxidants; phenolic components; have potential value
as chemo-preventative materials for human health (Islam
et al., 2009). Both beta-carotene and Vitamin C are very powerful
antioxidants that work in the body to eliminate free radicals. Nestel
et al. (2006) recorded the biofortification of staple food crops
is a new public health approach to control Vitamin A, iron and zinc deficiencies
in poor countries. Vitamin A deficiency has been recognized as a widespread
problem affected more than 700 million people, especially in developing countries.
Beta-carotene is the most available/important source of pro-vitamin A in the
diet of most people living in these countries (Sanusi and
Adebiyi, 2009). Orange-Fleshed Sweet Potatoes (OFSPs) which are naturally
rich in β-carotene, are an excellent food source of pro-vitamin A. These
varieties can make a significant contribution to a viable long-term effective
and sustainable food-based approach to prevent vitamin A deficiency in developing
countries (Hagenimana et al., 1999). Studies of
β-carotene during storage and processing of vegetables show no definite
trend of nutrient retention but fluctuate among samples analyzed in different
laboratories. Reports range from no loss to slight or marked decrease when total
carotenoids were measured. The OFSP 0ne of the biofortified crops especially
women and preschool children and one of important Millennium Development Goals
(SCN, 2004; Nestel et al.,
Sweet potato could be a good source of protein ingredient for food processing
as it possesses good solubility and emulsifying properties (Mu
et al., 2009). Food preservation prevent deteriorative reactions,
extends a food's shelf-life and assures is safety. Thermal processing has most
of the characteristics of an ideal food preservation (Chipurura
and Muchuweti, 2010).
The preservation of fruit by jam making is a familiar process carried out on
a small scale by housewives in many parts of the world. Processing fruits to
give a mixture set to a gel and good consistence jam is possible only after
perfect preparation (Singh et al., 2009). The
principle objectives of this study were determined the proximate composition
of sweet potatoes, processed and effected of storage period on stability of
MATERIALS AND METHOD
The genotypes of sweet potato; TDINUNG NO.64, CEMSA 74-228 and ZAPALO were
obtained from International Potato Center (CIP) and cultivated in Shambat horticultural
Station farm, Agricultural Research Corporation (ARC), Sudan during 2010 season.
Harvested sweet potatoes were stored at 15°C±2, 65-70% relative humidity
for 7 days. The raw material was washed, peeled and cutted (~2x2 cm); then were
immersed in hot water (60°C) for 10 min and then dipped in 1% ascorbic acid
solution for 30 min to prevent enzymatic browning of surface (Suliman
and Ismail, 2007) which was mixed with water (1:2) and pulped. Sweet potato
jam was processed using formula recommended by Singh et
Microbiological analyses: According to Kilcast and
Subramanian (2000) these products were subjected to microbiological analyses
to evaluate its safety and to determine the appropriate shelf life.
Physico-chemical analyses: Total Soluble Solids (TSS), pH-value, total
titratable acidity (as citric acid), ascorbic acid and minerals using methods
recorded by Ranganna (2001). While the moisture, protein,
fats, fiber, ash, reducing sugars and carbohydrates were determined according
to the AOAC (2000). The caloric values of the different
samples were calculated by summing the values obtained through multiplying the
contents of fats, protein and carbohydrates by the coefficients recorded by
Vitamin A: Vitamin A was determined according to the method described
by AOAC (2000).
B-complex group: A 15 g mostly of sweet potato were extracted with 25
mL of extraction solution (89% water+10% Methyl CN+1% Acetic acid) at 60°C
for 15 min cooled then filtered through Whatman No. 1 according to AOAC
(2000). An HPLC (model: Shimadzu, Japan, 2004) was used for the determination
of thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6) and folic acid.
Separation was achieved at ambient temperature on a Phenomenex Luna C18
(150x4.5 mm) analytical column. The flow rate was 0.8 mL min-1 and
the absorbance was measured at 280 nm. Detection limits were in the range of
1.6-3.4 ng, per 20 μL injection while linearity held up to 25 ng μL-1.
Theobromine (2 ng μL-1) was used as internal standard.
Minerals: The minerals (Ca, Fe, Mg, P, Na K and Zn) were determined
according to Ranganna (2001) using atomic absorption chromatography
(model: Carbolite-Bam ford S30 2 AU. Sheffield, England). Sodium was determined
using fame photometer (model: Instrument shimadzu-AA-6800).
Sensory evaluation: The sensory evaluation was carried out by the ranking
method described by Ali and El-Faki (2006).
Statistical analysis: Replicates of each sample were analyzed using
Statistical Analysis System (SAS). The Randomized Complete Design (RCD) was
adopted for this study. The Analysis of Variance (ANOVA) and least significant
difference (LSD at 5%) were used to separate the means according to Musa
RESULTS AND DISCUSSION
Table 1 shows chemical composition of raw sweet potato genotypes
expressed on dry basis. The results showed that no variations in the chemical
composition of the raw materials, except slight different in fiber and ash.
The moisture percentage of first genotype (TDINUNG NO. 64) was 36.12%, second
genotype (CEMSA 74-228) was 36.35% and of third genotype (ZAPALO) was 35.54%.
These results are lower than range of 51.80 to 77.10% recorded by Woolfe
(1992) and range of 69.20 to 70.80% suggested by Salami
et al. (2006). These variations may be due to the climatic differences.
The protein content of first, second and third genotypes were 15.09, 17.29
and 12.22%, respectively. The values of proteins are within the range from 13.76
to 18.18% stated by Salami et al. (2006). Nevertheless,
these values are greater than range from 0.30 to 10.00% reported by Salunkhe
and Kadam (1998).
|| Chemical composition of raw sweet potato genotypes
|*C: Crude, Carbs: Carbohydrate
This difference in protein content between genotypes implies that it could
be possible to breed and produce sweet potato with highly protein content.
Chemical analysis of the sweet potato genotypes showed that the first and third
genotypes had substantially greater percentage of crude fiber content (15.67
and 14.31%, respectively), than the second genotype (9.19%). The result of first
and third genotype is superior to range 9.77 to 13.02%, whereas, the result
of second type is comparable to that range recorded by Salami
et al. (2006).
As can be seen in Table 1 the content of ash of three genotypes.
ZAPALO had higher ash content of 12.05%, than TDINUNG NO. 64 of 10.83% and CEMSA
74-228 of 9.90%. These data are within the range of 9.94-12.86% (Salami
et al., 2006). Results show that TDINUNG NO. 64, CEMSA 74-228 and
ZAPALO sweet potatoes contain fats 1.63, 1.20 and 1.28%, respectively. The fats
content of sweet potato of 1.30%, obtained by Dauthy (2009)
in agreement with result obtained by third genotype. The genotypes under investigate
containing 56.82, 62.42 and 60.14% carbohydrates content, respectively. Dauthy
(1995) suggested inferior content (27.30%) than those obtained in this study.
All the findings of the proximate analyses obtained in this study were highest
than results of 21 Caribbean sweet potato genotypes recorded by Adebisolo
et al. (2009).
The contents of Vitamin C of three genotypes (65.70, 60.08 and 63.27 mg/100
g, respectively) are richer than range of fourteen sweet potato cultivars of
9.50 to 25.00 mg/100 g stated by Woolfe (1992). These genotypes containing a
large amount of energy for human body, equal to 305.98, 334.12 and 305.78 k
cal/100 g for TDINUNG NO. 64, CEMSA 74-228 and ZAPALO, respectively. These findings
of energy value were higher than those reported by Salunkhe
and Kadam (1998) and which might be attributed to differences between carbohydrates,
protein and fat values.
Table 2 shows the vitamin A and contents of B-complex group
of fresh sweet potatoes under study. Vitamin A content of TDINUNG NO. 64, CEMSA
74-228 and ZAPALO were 225.27, 148.65 and 217.83 μg/100 g retinol equivalent,
respectively. The findings of all genotypes within the range of 100-1600 μg/100
g RE obtained by Low et al. (2007). Beta-carotene-rich
orange-fleshed sweet potato is an excellent source of pro-vitamin A. in developing
countries; sweet potato is a secondary staple food and may play a role in controlling
Vitamin A deficiency (Jaarsveld et al., 2005).
TDINUNG NO. 64, CEMSA 74-228 and ZAPALO sweet potato genotypes are containing
1.45, 0.16 and 1.08 mg/100 g of B1; 0.37, 0.10 and 0.30 mg/100 g of B2; 12.44,
5.43 and 10.25 mg/100 g of B3; 1.58, 0.22 and 1.29 mg/100 g of B6 and lastly
0.19, 0.01 and 0.07 mg/100 g of folic acid, respectively. These results are
agreement with results of OFSPs recorded by Suliman and
Moreover, the minerals profiles of sweet potatoes were presented in Table 3. From the tabulated data it is obvious that the genotypes are rich in many minerals. CEMSA 74-228 has highest levels of iron, magnesium, phosphorus, sodium and potassium of 0.64, 21.60, 44.63, 15.72 and 352.00 mg/100 g, respectively. While TDINUNG NO. 64 have highest level of zinc of 0.32 mg/100 g.
|| Vitamins A and B-complex content of the fresh sweet potato
The samples of products investigated were free from bacterial or fungal contamination
during 12 months ambient storage. The physico-chemical characteristics of three
genotypes jams at zero time (initial) were within the range recommended range
for jam manufacture by CODEX (2006, 2002).
The significant difference (p≤0.05) of chemical and physical-chemical properties
of jams during storage is as shown in figures below. There is little significant
difference (p≤0.05) in TSS% was observed during storage period, from 69.00
to 68.50%, 70.00 to 69.00% and 68.00 to 68.50% for TDINUNG NO. 64, CEMSA 74-228
and ZAPALO, respectively (Fig. 1). These results were in agreement
with the findings of Yildiz et al. (2011).
The jams processed from sweet potato genotypes showed an increase in pH throughout
storage period (Fig. 2). The initial values were 2.67, 2.61
and 2.67; the final values were 2.95, 2.83 and 2.80. Consequently, the total
titeratable acidity decreased toward the end of storage time for three types
of jam, when initial (0.51, 0.63 and 0.53%, respectively) and final (0.44, 0.55
and 0.41%, respectively) times were compared. The relationship between total
titeratable acidity behavior and storage time was illustrated in Fig.
3. This losses were agrees with losses recorded for some fruit jams during
storage (Khan, 1989).
After 12 months storage (Fig. 4), the total sugars of jams
were significantly (p≤0.05) decreased from 67.54 to 66.81% (first jam), 66.63
to 64.51% (second jam) and from 68.70 to 67.00% (third jam). The loss of total
sugars may be explained by non enzymatic browning reactions. Yousif
and Alghamdi (2000) reported the same behavior during stored jam from some
Saudi date cultivars.
|| Minerals content (mg/100 g) of sweet potato genotypes
||Effects of storage period on total soluble solids of sweet
potato jams. Where: A: TDINUNG No. 64, B: CEMSA 74-228 and C: ZAPALO
||Effects of storage period on pH-value of sweet potato jams.
Where: A: TDINUNG No. 64, B: CEMSA 74-228 and C: ZAPALO
||Effects of storage period on total acidity of sweet potato
jams. Where: A: TDINUNG No. 64, B: CEMSA 74-228 and C: ZAPALO
||Effects of storage period on total sugars of sweet potato
jams. Where: A: TDINUNG No. 64, B: CEMSA 74-228 and C: ZAPALO
|| Sensory evaluation quality of sweet potato jams
|Values having different superscript letters in columns and
rows are significantly different (p≤0.05)
Furthermore, Table 4 shows results of sensory evaluation quality of sweet potato jam compared to jam obtained from market (control). The panelists were preferred sweet potato jam processed from TDINUNG NO. 64, followed ZAPALO jam, followed CEMSA 74-228 jam and lastly the control jam (market sample). These jams had a good natural color appearance, with evident significant (p≤0.05) differences in flavor, taste and consistency between the control jam and sweet potato jams. TDINUNG NO. 64 recorded highest values of color (62 score), taste (57 score) and consistency (60 score); while the control recorded the highest value of flavor (55 score) and lowest values of color, taste, consistency and overall quality of 40, 42, 40 and 41 scores, respectively.
It can be concluded that orange-fleshed sweet potatoes can ply a remarkable role in the human diet since it contains an excellent amount of vitamin A, a good source of carbohydrates, Vitamin C and B high. Also, support the body with many minerals. On the other hand, like other fruits jam, sweet potatoes observed best quality nutritious jam and were found most beneficial by securing microbial safety, physico-chemical stability and highest score during 12 months storage at ambient temperature.
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